1. Field of the Invention
The present invention relates to a display device and method of fabricating a display device, and more particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device.
2. Description of the Related Art
In flat panel display devices having active devices, such as a liquid crystal display (LCD) devices, thin film transistors (TFTs) are disposed in each pixel region to drive pixel cells in the display device. A driving method using the TFTs is commonly referred to as an active matrix driving method, wherein the active devices are placed within each pixel region and are arranged in a matrix configuration to drive the individual pixel cells.
FIG. 1 is a plan view of an LCD device according to the related art. In FIG. 1, an LCD device includes an N×M-number of pixels arranged along vertical and horizontal directions, wherein each pixel includes a TFT 10 formed at crossing regions of a gate line 3, which receives a scan signal from an external driving circuit, and a data line 5, which receives an image signal. The TFT 10 includes a gate electrode 11 connected to the gate line 3, a semiconductor layer 12 formed on the gate electrode 11 to be activated by a scan signal supplied to the gate electrode 11, and source and drain electrodes 13 and 14 formed on the semiconductor layer 12. In addition, a pixel electrode 16 is formed within a display region of the pixel and is connected to the drain electrode 14 to drive liquid crystal molecules according to the activation of the semiconductor layer 12.
FIG. 2 is a cross sectional view along I-I′ of FIG. 1 according to the related art. In FIG. 2, the TFT 10 is formed on a first substrate 20 made of a transparent material, such as a glass, and includes the gate electrode 11 formed on the first substrate 20, a gate insulating layer 22 deposited over the first substrate 20, the semiconductor layer 12 formed on the gate insulating layer 22, the source and drain electrodes 13 and 14 formed on the semiconductor layer 12, and a passivation layer 24 disposed over an entire area of the first substrate 20. In addition, a pixel electrode 16 is formed on the passivation layer 24 and is connected to the drain electrode 14 through a contact hole 26.
In FIG. 2, a black matrix 32 and a color filter layer 34 are formed on a second substrate made of a transparent material, such as glass. The black matrix 32 is formed in a non-display region, such as the TFT forming region, and in a region between pixels to block light transmission in the non-display region. In addition, the color filter layer 34 includes red (R), green (G), and blue (B) layers formed on the second substrate 30, wherein the first and second substrates 20 and 30 are bonded together with a liquid crystal material layer 40 formed therebetween.
FIGS. 3A-3I are cross sectional views of a method of fabricating an LCD device according to the related art. In FIG. 3A, a metal layer 11a is deposited on a first substrate 20 (i.e., TFT substrate), and a photoresist layer 60a is deposited on the metal layer 11a, wherein the deposited photoresist layer 60a is then baked at a certain temperature. Next, a mask 70 is positioned above the baked photoresist layer 60a, and light, such as ultraviolet light, is irradiated onto the photoresist layer 60a. 
In FIG. 3B, a developer is applied to the photoresist layer 60a, thereby forming a photoresist pattern 60 on the metal layer 11a. Accordingly, since the photoresist is a negative photoresist, regions that are not affected by the ultraviolet light are removed by the developer.
In FIG. 3C, a portion of the metal layer 11a covered by the photoresist pattern 60, is removed by applying an etchant to the metal layer 11a. Accordingly, a gate electrode 11 is formed on the first substrate 20.
In FIG. 3D, a gate insulating layer 22 is formed over the first substrate 20 and a semiconductor layer 12a is formed thereon. Then, a photoresist layer is deposited on the semiconductor layer 12a and ultraviolet light is irradiated onto the photoresist layer using a mask. Next, a developer is applied to portions of the photoresist layer that may been irradiated with the ultraviolet light to form a photoresist pattern 62 on the semiconductor layer 12a. 
In FIG. 3E, an etchant is applied to the semiconductor layer 12a using the photoresist pattern 62 as an etch-blocking mask to form a semiconductor layer 12 on the insulating layer 22.
In FIG. 3F, a metal layer (not shown) is deposited on an entire surface of the first substrate 20, and a photoresist pattern (not shown) is formed on the metal layer using a mask. Then, the metal layer is etched using the photoresist pattern as an etch-blocking mask to form source and drain electrodes 13 and 14 on the semiconductor layer 12.
In FIG. 3G, a passivation layer 24 is deposited on the first substrate 20 including the source and drain source electrodes 13 and 14. Then, a portion of the passivation layer 24 formed on the drain electrode 14 is etched using the photolithographic processes described above, thereby forming a contact hole 26 exposing a portion of the drain electrode 14.
In FIG. 3H, a transparent material, such as indium tin oxide (ITO), is deposited on the passivation layer 24 and etched using the above-described photolithographic processes to form a pixel electrode 16 on the passivation layer 24. In addition, the pixel electrode 16 is electrically connected to the drain electrode 14 via the contact hole 26 formed in the passivation layer 24.
In FIG. 3I, a black matrix 32 and a color filter layer 34 are formed on a second substrate 30 (i.e., color filter substrate), and the first and second substrates 20 and 30 are bonded together with a liquid crystal material layer 40 sandwiched therebetween.
Accordingly, as described above, the source and drain electrodes 13 and 14 and the semiconductor layer 12 are formed using photolithographic processes including the photoresist layers. However, using the photoresist layers is problematic. For example, the photolithographic processes are complicated since the photoresist patterns are formed through repeated processing including photoresist depositing, baking, irradiating, and developing. In addition, the baking process actually includes a soft baking process and a hard baking process that are performed at separate temperatures.
Moreover, since the fabrication processes include forming of a plurality of patterns (or electrodes), a plurality of photoresist processes are required. Accordingly, since photoresist processing must be performed to create each of the patterned lines, fabrication costs increase. For example, the fabrication costs of the photoresist process are approximately 40-45% of a total cost of the TFT substrate process.
Furthermore, the fabrication processes generate significant amounts of environment contaminants. In general, since the photoresist layer is formed by deposited photoresist material using a spin coating method, most of the photoresist material may be discarded. Accordingly, the discarded photoresist material increases fabrication costs of the TFT substrate and introduces contaminants into the environment.
In addition, performance of the LCD device may degrade due to remnant amounts of the photoresist material. For example, since the photoresist material is coated using the spin coating method, it is difficult to control a thickness of the photoresist layer. Accordingly, the photoresist layer has a non-uniform thickness and portions of the photoresist layer may remain after the photoresist pattern is supposed to be completed removed.